For the last twenty years, many improvements have been made in the art of ink jet imaging. The quality of the imaging has improved, and the speed of that imaging has increased. The number of type fonts available has grown to over 200. The image density has increased to 240 dots per inch. The design of the equipment used to perform ink jet imaging has also improved several times.
One limitation of this process has been present since the use of ink jet imaging first began. This limitation concerns the inability to successfully image with ink jet ink onto areas of a substrate having a heavy coverage of press ink. The ink jet ink, which is typically aqueous based, and the press ink, which is typically organic based, are incompatible in part because of a difference in surface tension between the two. This difference in surface tension generally causes ink jet ink to bead up on the surface of areas of a printed article having a heavy coverage of press ink when the ink jet ink is applied directly to the layer of press ink. This beading of the ink jet ink provides the article with an unsightly mottled appearance. Further, once the ink jet ink beads up on the surface of the press ink, the ink jet ink easily smears and/or wipes off of the printed article rendering the article useless. This limitation particularly affects industries which mass produce printed articles such as personalized forms, mailers, bar coded addresses, advertisements and other similar articles.
It is common in the art either to "reverse out" (i.e. leave unprinted) areas which are to be ink jet imaged or to not print valuable information, such as name and address, on any areas of a substrate which have areas of heavy coverage of press ink. Currently in the art, it is possible to ink jet image on areas of press ink coverage but such imaging is limited to areas having a maximum press ink print density of a 30% screen. An area of press ink coverage of a 30% screen has a pale pastel-like appearance which is undesirable for most printed articles. Any higher print density of press ink results in the ink jet ink easily smearing and, often, running off of the printed article. To ensure proper application of ink jet ink to an article which will have areas which are covered with press ink, the areas which are to be ink jet imaged will preferably receive no coverage of press ink.
Additionally, a heavy basis weight paper, such as 60 lb./ream offset paper, is required for ink jet imaging. When an offset paper having a basis weight less than 60 lb./ream is used, the ink jet ink penetrates the paper and shows through to the opposite side of the paper from the printed side. This results in the production of an unattractive and often useless printed article, especially if the article is to be ink jet imaged on both sides of the paper. Because one factor considered when purchasing paper is its price per basis weight, the use of high basis weight paper for a printed article increases the price of the final printed article.
For these reasons, a need has developed in the art for a method of imaging with ink jet ink on areas having heavy press ink coverage and a printed article which includes ink jet imaging on heavy press ink coverage areas. A need has also developed for a method of ink jet imaging on lower basis weight paper to decrease the price of a printed article.